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The Challenges of Meeting Iron Needs During Pregnancy

By Julia Bird

Yesterday, TalkingNutrition discussed the importance of folic acid for prenatal nutrition. Today, a second nutrient important for pregnant women is on the menu: iron. Why is iron so important? Pregnant women are at high risk of low blood iron because they must produce a large volume of blood over a short period of time to support the placenta and growing fetus. Cao and O’Brien estimate that women need to absorb 500 - 1200 mg of iron over the second and third trimesters of pregnancy. This translates to 3 mg to 8 mg absorbed iron per day. Assuming that iron absorption is in the range of 10 to 30%, this is an amount that could be obtained by the diet assuming that women meet requirements and that absorption occurs at the expected level. Women with adequate iron stores also have a buffer in case they cannot meet iron needs from diet alone during the second trimesters of pregnancy.

Poor iron status in women has been linked with higher rates of maternal mortality, reduced ability to withstand excessive blood loss in pregnancy, postpartum infection and fatigue (see review by Allen). Infants of iron deficient mothers are at greater risk of preterm delivery, low birth weight, and possible irreversible cognitive impairment. It is very important for women and their infants that maternal iron status is adequate to sustain the demands of pregnancy.

Zhao and co-workers recently reported on a clinical trial conducted in rural China of around 1600 mother infant pairs that were randomly assigned to either folic acid, or folic acid with iron during the second and third trimesters of pregnancy. The women supplemented with iron were given the equivalent of 60 mg iron per day as ferrous sulfate. The authors found that the intervention significantly reduced the risk of anemia (hemoglobin <110g/L), iron deficiency (serum ferritin <15µg/L or body iron <0 mg/kg), and iron deficiency anemia (meeting criteria for both anemia and iron deficiency). Even so, around half of iron supplemented women still had iron deficiency at the end of pregnancy, compared to three quarters of the women not taking iron. Iron deficiency anemia rates were halved by the iron supplement, but still around 10% of women taking iron supplements in the second and third trimesters of pregnancy had iron deficiency anemia.

These results show that an iron supplement taken during pregnancy can reduce the risk of poor iron status. However, an iron supplement taken during pregnancy may not be enough. There are limits to the amount of iron that women can absorb. Timing may be important. These women were only supplemented during the second two trimesters of pregnancy. Even at enrolment, 20% of women had iron deficiency and 10% had anemia. What would the results have been if women were supplemented during the months before conception? The months before pregnancy are considered to be part of the “first thousand days” that are important for children to live a healthy and productive life. Achieving adequate body iron stores before pregnancy may be most effective in reducing rates of low iron.